Madvise

MADV_FREE Marks Anonymous Pages for Lazy Reclaim

MADV_FREE does not immediately replace a private anonymous page with zeros. It marks eligible pages as disposable, allowing Linux to reclaim them later. Until reclaim actually occurs, existing bytes can remain observable. A write before reclaim cancels the disposable state for the affected page. That timing makes MADV_FREE distinct from advice that immediately changes the process-visible state of a range. It is a lazy reclamation contract: the application declares that old contents are expendable, while the kernel chooses when physical memory is recovered.